In American politics, times of great crisis traditionally cool the fevers of partisan rancor and turn enemies, albeit temporarily, into allies. That's one of the ways in which the aftermath of Sept. 11, 2001, evokes echoes of the period following Dec. 7, 1941.But history also teaches that such unity, like the friendships which it fosters, can be ephemeral. Once the common threat that created them begins to fade, alliances are likely to unravel. Then, latent ideological animosities are inevitably resurrected, brand-new political ambitions come into play and, in a flash, comrades who stood shoulder to shoulder find themselves rolling in the dirt trying to gouge each other's eyeballs out. In "Harry and Ike," journalist Steve Neal examines one such famous partnership - between the two shrewd and remarkably similar men from the middle of America, one a Democrat and the other a Republican, who became the nation's 33rd and 34th presidents. It was, as Mr. Neal says in his subtitle, a "partnership that remade the postwar world." It was built on a shared vision of that world and America's place in it, on the partners' similar backgrounds and experiences, and on their personal congeniality and mutual respect. But it did not endure. Politics set in, egos were bruised and the partnership dissolved. So did the friendship between the partners, although it was eventually, and rather touchingly, re-established late in their lives. Historians often observe that even for the most sentient people, the 20 years or so from just prior to their birth until their early teens is a sort of dead spot in their historical understanding. For that reason alone, Mr. Neal's thoroughly reported look at the 24-year association between Harry S. Truman and Dwight David Eisenhower ought to be of particular interest to Americans now aged from about 40-60 - the extended boomer generation. Many of us probably know less about postwar America than we do about the Civil War. We probably do know, though, that Truman was born in Missouri and Eisenhower, six years later, in Kansas; that each grew up poor but proud, used to hard work and was fond of reading history; that each served in World War I (though only Truman saw combat); and that each, throughout his career, was not only frequently underestimated, but also knew how to take advantage of that. The underestimation came especially from the political left, which makes a specialty of it. Though they had been working their way up the greasy poles of politics and the military for years, it was not until 1944 that Truman, as Franklin Delano Roosevelt's fourth-term vice president, and Eisenhower, as the architect of the Normandy invasion, first appeared in the national spotlight. Five years later, polls indicated that their countrymen considered them, respectively, the first and second most admired men in the world, just ahead of Winston Churchill. Friction between two such towering figures would seem likely, but there was no sign of it - yet. After V-J Day, Truman and Eisenhower had worked closely together on such volatile matters as slowing the pace of postwar demobilization; universal military training (they supported it against an odd alliance of organized labor and conservative Republicans); the Marshall Plan for rebuilding Europe and the unification of the military services under a new Department of Defense. Not only did they hold similar views on many policy questions, but the two men liked one another, enjoying a bourbon together from time to time at the White House and carrying on a cordial private correspondence. Even beyond that, they needed one another's help in very different ways. Politically, the presence of revered and ostensibly nonpartisan Eisenhower at this side was enormously valuable to Truman, especially in dealing with the Congress, and he often took advantage of it. The president responded not only with friendship and flattery for the general, but by personally intervening to win Eisenhower a special tax ruling on the proceeds from his book, "Crusade in Europe." Under the ruling, as Mr. Neal describes it, the $635,000 Ike received from Doubleday, his publisher, could be considered a capital gain and taxed at the rate of 25 percent, instead of the confiscatory 75 percent rate then applied to ordinary income. The difference, in the dollars of the time, made Eisenhower rich. Merited though it may have been, it was a considerable presidential favor. The Harry-and-Ike friendship broke down, not when Truman ran in 1948 and Eisenhower decided not to, but four years later, when those decisions were reversed. Once Eisenhower openly declared himself Republican, the old cordiality quickly slipped away, and for more than a decade, including the entire Eisenhower presidency, relations between the two were strained. But time can heal. When they were both ex-presidents, secure in their nation's esteem, respect and affection between the two were restored and lasted until Eisenhower's death in 1969. Steve Neal's account of the Truman-Eisenhower partnership is warm, understanding and remarkably detailed. It's a fine portrayal of one of the most significant political and personal relationships in postwar American history. It's also a reminder that bipartisan alliances, no matter how productive, are invariably fragile.